A variety of devices have been used for stirring molten metal directly in the bath of a melting or holding furnace. This invention proposes a device for gas dynamical stirring of molten metals, such as aluminum and its alloys, which is both effective in operation and simple in construction.
A device for stirring molten metal usually comprises a refractory-lined pipe with a removable cover, a system for feeding compressed air into the pipe interior, and a system for building up vacuum therein.
This type of device is mounted in the wall of a melting unit through a port, disposed above the level of molten metal, in a manner to permit the lower end of the pipe to be immersed in the melt. The device incorporates level gauges connected to the control circuit of the compressed gas supply system and vacuum building-up system. This device is similar in operation to a pump or ejector which uses a pulse of compressed gas acting on the entire body of molten metal. The procedure of stirring a body of molten metal comprises the steps of alternately withdrawing molten metal upwardly from the body in a confined space to a level above the body and expelling the withdrawn molten metal into the body as a submerged high velocity jet. The alternate metal-withdrawing and metal-expelling steps are effected by alternately applying suction and gaseous fluid (gas) under pressure in the confined space above the body of molten metal. The jet of expelled metal creates turbulence in the body of molten metal and thus effects its stirring.
The prior-art method makes it possible to enhance production efficiency of a melting or holding furnace. In addition, the quality of metal being stirred is improved by maintaining uniform chemical composition and temperature throughout the melt bath. Jets of molten metal forcefully expelled from the ejector are poured over lumps of solid charge in a furnace to thereby enable their rapid melting.
On being tapped from a melting or holding furnace, the molten metal is further subjected to refining by means of gas, for example, argon.
However, gas-dynamic pumps used for stirring molten metal fail to ensure optimum conditions for obtaining hihg-quality metal by way of reducing the amount of gas, as well as slag and oxide inclusions contained therein.
Attempts to effect refining of metal by applying a pulse of compressed gas thereto have ended so far in failure by reason of extremely short time of contact between gas and the surface of metal jet in the interior of a stirrer pipe during metal-expelling procedure.
U.S. Pat. No. 3,895,937 discloses a method according to which a jet of molten metal discharged from a melting furnace into a vacuum holding furnace is rifined by means of gas. However, this method also fails to ensure sufficiently high quality of metal due to a short time period during which refininf gas remains in contact with molten metal.
The known devices currently used for stirring and refining molten metal fail to meet ever growing demands for higher throughout capacity of melting furnaces and improved quality of metal. In other words, more sophisticated devices are needed today to satisfy increasing demands of modern industry.
Moreover, a demand has arisen for high-purity metals intended for the manufacture of vital units and parts to find wide application, for instance, in the aircraft industry.